python vtk 通过回调函数监测键盘”Up”键动作，每按一次方向上键，actor变换一种颜色

import vtk

class KeyPressInteractorStyle(vtk.vtkInteractorStyleTrackballCamera):

    def __init__(self,parent=None):
        self.parent = vtk.vtkRenderWindowInteractor()
        if(parent is not None):
            self.parent = parent

        self.AddObserver("KeyPressEvent",self.keyPress)

    def keyPress(self,obj,event):
        key = self.parent.GetKeySym()
        if key == 'Up':
            #产生随机颜色
            r = vtk.vtkMath.Random(., 1.0)
            g = vtk.vtkMath.Random(., 1.0)
            b = vtk.vtkMath.Random(., 1.0)
            actor.GetProperty().SetColor(r, g, b)
            #下面这一行是关键，实现了actor的更新
            renWin.Render()

#在此处修改几何类型
cube = vtk.vtkCubeSource()

mapper = vtk.vtkPolyDataMapper()
mapper.SetInputConnection(cube.GetOutputPort())

actor = vtk.vtkActor()
actor.SetMapper(mapper)
#修改actor初始颜色
actor.GetProperty().SetColor(1.0, 1.0, 1.0)
#修改actor初始状态旋转角度
actor.RotateX(30.0)
actor.RotateY(-45.0)

ren = vtk.vtkRenderer()
renWin = vtk.vtkRenderWindow()
renWin.AddRenderer(ren)
iren = vtk.vtkRenderWindowInteractor()
iren.SetRenderWindow(renWin)

iren.SetInteractorStyle(KeyPressInteractorStyle(parent = iren))

ren.AddActor(actor)
#修改背景颜色
ren.SetBackground(0.1, 0.2, 0.3)
#修改窗口大小
renWin.SetSize(, )

iren.Initialize()

ren.ResetCamera()
ren.GetActiveCamera().Zoom(1.5)
renWin.Render()

iren.Start()